rcu,cleanup: move synchronize_sched_expedited() out of sched.c

The first version of synchronize_sched_expedited() used the migration
code in the scheduler, and was therefore implemented in kernel/sched.c.
However, the more recent version of this code no longer uses the
migration code, so this commit moves it to the main RCU source files.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
diff --git a/include/linux/rcutree.h b/include/linux/rcutree.h
index c0e9683..3a93348 100644
--- a/include/linux/rcutree.h
+++ b/include/linux/rcutree.h
@@ -48,6 +48,7 @@
 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
 
 extern void synchronize_rcu_bh(void);
+extern void synchronize_sched_expedited(void);
 extern void synchronize_rcu_expedited(void);
 
 static inline void synchronize_rcu_bh_expedited(void)